updated placeholder hook to define immutability and null contracts, deprecated online player function

src/main/java/me/clip/placeholderapi/PlaceholderHook.java

@@ -22,33 +22,43 @@ package me.clip.placeholderapi;
 
 import org.bukkit.OfflinePlayer;
 import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
-public abstract class PlaceholderHook {
+public abstract class PlaceholderHook
+{
 
-    /**
-     * called when a placeholder value is requested from this hook
-     *
-     * @param player {@link OfflinePlayer} to request the placeholder value for, null if not needed for a
-     *               player
-     * @param params String passed to the hook to determine what value to return
-     * @return value for the requested player and params
-     */
-    public String onRequest(OfflinePlayer player, String params) {
-        if (player != null && player.isOnline()) {
-            return onPlaceholderRequest((Player) player, params);
-        }
+	/**
+	 * called when a placeholder value is requested from this hook
+	 *
+	 * @param player {@link OfflinePlayer} to request the placeholder value for, null if not needed for a
+	 *               player
+	 * @param params String passed to the hook to determine what value to return
+	 * @return value for the requested player and params
+	 */
+	@Nullable
+	public String onRequest(@Nullable final OfflinePlayer player, @NotNull final String params)
+	{
+		if (player != null && player.isOnline())
+		{
+			return onPlaceholderRequest((Player) player, params);
+		}
 
-        return onPlaceholderRequest(null, params);
-    }
+		return onPlaceholderRequest(null, params);
+	}
+
+	/**
+	 * called when a placeholder is requested from this hook
+	 *
+	 * @param player {@link Player} to request the placeholder value for, null if not needed for a player
+	 * @param params String passed to the hook to determine what value to return
+	 * @return value for the requested player and params
+	 */
+	@Nullable
+	@Deprecated
+	public String onPlaceholderRequest(@Nullable final Player player, @NotNull final String params)
+	{
+		return null;
+	}
 
-    /**
-     * called when a placeholder is requested from this hook
-     *
-     * @param player {@link Player} to request the placeholder value for, null if not needed for a player
-     * @param params String passed to the hook to determine what value to return
-     * @return value for the requested player and params
-     */
-    public String onPlaceholderRequest(Player player, String params) {
-        return null;
-    }
 }